Azeotropic distillation method



United States Patent Ollice lnlldfibd Patented Dec, 17, l953 3,114,686AZEU'I'ROPIC DETELLA'EIQN METHQD Art C. McKinnis, North Long Beach, andliving B. Webb,

Yorba Linda, (lalih, amignors to Union Gil Coin any at (California, LosAngeles, Calif., a corporation of California Filed fiept. 29, 1961, Sen.No. 141329 29 Claims. (Cl. 262-42) This invention relates to therecovery of naphthalenic hydrocarbons from mixtures comprising the same,and in particular concerns a method of treating hydrocarbon mixturesboiling Within the 390-520 F. range and containing naphthalene and/ oralkyl-substituted naphthalenes for the purpose of recovering saidnaphthalenic hydrocarbons in concentrated form.

The expanding use of naphthalene and alkylnaphthalenes for theproduction of dicarboxy-lic acids useful in manufacturing syntheticresins and fibers has created considerable interest in the recovery ofthese naphthalenic hydrocarbons from hydrocarbon fractions of petroleumorigin. It is well known that certain fractions obtained from petroleumrefining operations, e. g., catalytic cracking and reforming, containconsiderable quantities of naphthalene and ailiylnaphthalenes. However,such fractions also contain large quantities of other hydrocarbon typeswhich have boiling points very close to those of the aforesaidnaphthalenic hydrocarbons or which form azeotropes therewith. In eithercase, satisfactory separation of the naphthalenic from thenon-naphthalenic hydrocarbons cannot be accomplished by fractionaldistillation.

Accordingly, the principal object of the present invention is theprovision of an improved method for treating hydrocarbon mixturesboiling within a 390 520 F. range and comprising naphthalene and/oralkylnaphthalenes to separate said naphthalenic materials fromnon-naphthalsnic hydrocarbons pre ent in the mixture. A more particularobject of the invention is to provide a method whereby non-naphthalenichydrocarbons boiling in the naphthalene range, that is, within the rangeof about 490 450 F, can be readily separated from mixtures of suchhydrocarbons with naphthalene. Other and related objects will becomeapparent to those skilled in the art as the description of the inventionproceeds.

We have discovered that the above objects and attendant advantages canbe realized in an azeotropic distillation process in which a glycoliormate is employed as the azeotrope former. More particularly, we havefound that the glycol for-mates form azeotropes of unusually low boilingpoint with non-naphthalenic hydrocarbons boiling within the 396 -520 F.range, so that by admixing a glycol forrnate with a mixture comprisingnaphthalenic and non-naphthalenic hydrocarbons boiling within saidrange, and subjecting the resulting mixture to distillation, anexceptionally etlicient separation of the two types of hydrocarbons canbe achieved. The non-naphthalenic hydrocarbons distill overhead in theform of low-boiling azeotropes with the glycol formate, leaving thenaphthalenic rnatcria behind as distillation bottoms. The azeotropicdistillate is rich in hydrocarbons and has a relatively low heat ofvaporization, so that the amount of heat required to separate a unitvolume of non-naphthalenic hydrocarbons from the feed mixture isrelatively low.

We have discovered that the glycol fornlates exhibit a highly selectiveaction toward the non-naphthalenic hydrocarbons when employed asazeotrope formers in the above manner and hence lower reflux ratios andfewer plates in the distillation column are required to eiicct thedesired separations. Moreover, the glycol formates form two phases withnon-naphthalenic aromatic hydrocarbons taken overhead, so that in manyinstances substantially complete separation of the azeotrope former fromthe distillate can be achieved by simple gravity settling, without thenecessity of utilizing elaborate secondary equipment for that purpose.Following removal of non-mph thalenic hydrocarbons, the naphthalenecontained in the remaining bottoms fraction can be easily recovered bynon-azeotropic distillation, or by any other desired means.

Considering now the process of our invention in greater detail, thefeedstock entering said process may be any mixture of hydrocarbonscorn-prising naphthalene and/ or alliylnaphthalenes and at least onenon-naputhalenic hydrocarbon which cannot be separated from thenaphthalenic components by simple fractional distillation. The termnaphthalenic hydrocarbon is herein employed to designate a hydrocarboncompound whose molecule contains the characteristic naphthalene groupinz Conversely, the term non-naphthalenic hydrocarbon designates ahydrocarbon compound whose molecule does not contain said grouping.Thus, the non-naphthalenic hydrocarbons which may be present in thefeedstock include aliphatic compounds such as dodecane and higherisomeric parafiins and corresponding oletins; naphthenic compounds suchas cyclohertylheptene, hexylcyclohenane, dicyclohexyl, anddecahydronaphthalene; benzenoid compound such as triethylbenz ne,dinietnylindane, ethylindene, etc; and partially hydro .atednaphthalenic h3- drocarbons such as methyltetralin, dimethyltetralin,dihydronaphthalene eand methyldihydronaphthalene. The naphdlalenichydrocarbons which may be present in the feedstock include naphthalene,the methylnaphthalenes, the dimethylnaphthalenes, the ethylnaphthalenes,the isopropylnap thaienes, etc.

While the hydrocarbon feedstocks to the process of our invention cancontain any or all of the above-narned compounds, the prc-cess isparticularly applicable for the treatment of hydrocarbon mixturescontaining naphthalene and contaminated mainly with aromatichydrocarbons such as alkylbenzenes, alkyltetralins, alkyiindanos, andthe like, boiling within the naphthalene range and thereabouts, e.g.,from about 400 to about 456' h. it is known that naphthalene fractionscontaining like-boiling paraffin hydrocarbons can be purified byazeotropic distillation with various azeotroping agents. However, a moredifficult problem of separation is involved in mixtures such as thosejust named contaminated mainly with aromatic hydrocarbons. Petroleumfractions of this nature be derived from various hydrocarbon conversionand refining processes commonly used in the industry, such as forexample, catalytic re or-ming, catalytic cracking, thermal "ing and thelike. in particular, catalytic reforming ,hthas produces a heavyreformate fraction boiling above about 400 E, which contain from about40 to about 80% naphthalene and 'nethylnaphthalenes. The remaininghydrocarbons in this fraction are largely alkylbenzenes, tetralins,indanes, and the like. Sometimes a significant proportion of naphthenesand parafiins are present. The recovery of substantially purenaphthalene from such petroleum fractions presents a difficult problem.Simple fractional distillation is impractical because of the closeproximity of boiling points of the contaminating hydrocarbons, and alsothe formation of complex azeotropes.

The feedstocks suitable for treatment as taught herein are not limitedto those of conventional petroleum refinin origin and may be from anysource such as, for example, from destructive distillation orhydrogenation of coal processes or shale oil processes. Usually,however, the feedstock will be of petroleum origin. While the feedstockmay be one boiling over the entire 390-520 F. range, it will usually beone boiling over only a selected portion of such range (e.g., the400-450 P. fraction described above or a fraction boiling at 450470 F.and comprising monomethylnaphthalenes, etc.) and may of course containsome components boiling somewhat below or (less desirably) above saidrange. The feedstock may also be one which has been pretreated to removepart of the naphthalenic components, e.g., it may be a dealkylatedpetroleum hydrocarbon reformate fraction from which at least part of thenaphthalene has been previously separated by crystallization.

It will be apparent to those skilled in the art that feedstocks boilingover the entire 390-520 F. range which contain both naphthalenic andnon-naphthalenic hydrocarbons distributed throughout that range do not,when subjected to our azeotropic distillation treatment, yield acontinuous azeotropic overhead. Instead the overhead will vary as thedistillation proceeds, sometimes being azeotropic and sometimesnaphthalenic, depending upon the composition of the liquid in the still.Accordingly, to make a practical naphthalenic-non-naphthalenicseparation of such mixtures by distillation means alone, it is necessaryeither first to separate the mixture into appropriate fractions bystraight distillation and then to distil azeotropically selectedfractions, or to practice a combined azeotropic-straight distillationtechnique on the feedstock mixture and separate the overhead productsinto azeotropic and straight distillate categories. The above procedurescan be practiced in numerous ways, incorporating batch, flow and hybridbatch-flow methods of operation, as will be apparent to those familiarwith the distillation art.

Best results are achieved in the practice of our invention when the feedto any given azeotropic' distillation step has a boiling point rangespread no greater than about 50 F. It is of course desirable, in manycases, to have much narrower boiling point spreads, as exemplified bythe monomethylnaphthalene fractions boiling from about 450 to about 470F. referred to above. In any event, it is generally true that thenarrower the boiling point spread of a feed fraction, the cleaner willbe the split between its naphthalenic and non-naphthalenic fractions inour azeotropic distillation operation. The boiling point range fromabout 390 to about 520 F. is sufiiciently broad to encompass the threenaphthalcnic hydrocarbon fractions, namely, the naphthalene fraction,the monomethylnaphthalene fraction and the dimethylnaphthalene fraction,most often encountered in naphthalene dealkylation feedstocks.

Our invention has particular utility for the treatment of hydrocarbonfractions fitting above-indicated categories which contain naphthalenefractions comprising naphthalene and non-naphthalenic hydrocarbonmaterial boiling within about F. thereof, and especially such petroleumfractions in which the naphthalene fraction boils over the entire rangefrom about 410 to about 450 F. and one or more of the alkylbenzenes,alkyltetralins and alkylindanes comprises the non-naphthalenichydrocarbon material. More specifically, petroleum fractions within theabove class which have been found particularly amenable to treatment bythe method of this invention are those boiling above about 400 F. whichinclude, as nonnaphthalenic hydrocarbons, alkylbenzenes, alkyltetralinsand a-lkylindanes boiling over the range from about 410 to about 435 F;heavy naphtha reformates boiling above about 400 F. and including anaphthalene fraction boiling over the range from about 410 to about 450P. which preferably contains alkylbenzenes, alkyltetralins andalkylindanes; and heavy naphtha reformates which have been subiected tocatalytic hydrodealkylation, boiling above about 400 F. and including anaphthalene fraction boiling over the range from about 410 to about 450R, which naphthalene fraction preferably contains alkylbenzenes,alkyltetralins and alkylindanes.

Procedure-wise, our process is carried out as a conventional azeotropicdistillation operation, and any of the techniques commonly applied tosuch types of operation are applicable to the present process. in itssimplest embodiment, namely, batch distillation, the process consistsessentially of adding to the feedstock suflicient glycol formate to formazeotropes with the non-naphthalenic components, and thereafterdistilling the mixture in a reasonably efficient distillation column.The azeotropic distillate is condensed and passed to a separator Wherethe condensate is allowed to separate by gravity into two phases, one ofwhich comprises the non-naphthalenic components of the feedstockcontaining a small quantity of glycol formate and the other of whichcomprises glycol formate containing a relatively small quantity ofdissolved non-naphthalenic hydrocarbons. Either or both of said phasesmay be redistilled or otherwise treated to recover the azeotrope formerfor reuse. The naphthalenic components of the feedstock are contained inthe bottoms fraction which constitutes the desired end product of theprocess.

In practicing the process of our invention on those naphthalene-aromatichydrocarbon feedstock mixtures for the separation of which it is mostapplicable, We have found that substantially all of the alkylbenzenes,alkyltetralins, and alkylindanes which boil within about 30 F. ofnaphthalene can be efliciently azeotroped overhead before anysubstantial amounts of naphthalene appear in the overhead product.Moreover, it is found thatthe azeotropic overhead is unexpectedly richin hydrocarbons, containing only about to about percent by weight ofglycol formate, thus minimizing the distillation load, and the amount ofazeotroping agent required.

Attention is now directed to the accompanying drawing, which illustratesschematically one method of practicing the azeotropic distillationprocess of this inven-' tion. The initial feedstock is brought inthrough line 2 and admitted to distillation column 4 wherein the primaryiazeotropic distillation takes place. Column 4- may be a conventionalfractional distillation column containing, for example, 2080 plates andmay be operated at overhead reflux ratios of, e.g., 1:1 to 20:1.Azeotroping is continued until essentially all of the non-naphthalenichydrocarbons boiling within about 10 F, and preferably 20 F., ofnaphthalene are distilled overhead. The overhead temperatures during theazeotropic distillation will usually range between about 335 and about360 F., the glycol formatcs themselves boiling within the range fromabout 335 to about 366 F. The azeotropic overhead is taken off throughline it and condensed in condenser ll, and the resulting condensate istransferred by line 10 to a liquid phase separator 12. To provide thedesired reflux ratio, a portion of the condensate in line It} may bediverted through line 16 and admitted to the top of column 4.

In phase separator 12, the condensate may separate spontaneously intotwo phases, or a small proportion of a miscibility reducing agent may berequired, depending upon the nature of the feed. If the feed is rich inlower alltylated aromatics a miscibility reducing agent is ordinari'lyrequired, but if it is rich in higher alkylated aromatics and/or innaphtheucs, adequate phase separation occurs spontaneously. Suitablemiscibility reducing agents include anti-solvents for the glycolformates, e.g., paraifinic or naphthenic hydrocarbons such as pentane,decane, cyclohexane or the like. Other suitable miscibility reducingagents are the lower glycols such as ethylene glycol, propylene glycol,etc. Preferably, the miscibility reducing agent should be easilyseparable, as by distillation, from the phase in which it is dissolved.

The glycol formate rich phase which stratifies in separator 12 willordinarily contain about 1 to about 25% by weight of dissolvedhydrocarbons, and this solution is continuously recycled via line 14back to a mid-point in distillation column The hydrocarbon rich phase inseparator 12 ordinarily will contain about 1 to about 15 percent byweight of dissolved glycol formate. This hydrocarbon rich phase is thentransferred via line to fractionating column 2%), from which the glycolformats is distilled overhead via line 22 as an azeotropic distillatewith a portion of the non-naphthalenic hydrocarbons, and condensed intoseparator The azeotropic distillate from column 26, as Well,incidentally, as that of column 4, is a minimum boiling azeotrope in thesense that the various azeotropic combinations involved are minimumboiling azeotropes. The non-naphthalenic hydrocarbons are withdrawn asbottoms frorn column 253 la line 24.

A naphthalene-containing bottoms fraction is continuously withdrawn fromdistillation column 4 via line 26, and transferred to naphthalenefractionating column 23. Since substantially all of the close-boilingnon-naphthalenic hydrocarbons have been removed in column 4, theprincipal separation which is achieved in column 28 is normally theseparation of naphthalene from alkyl-naphthalenes such as for example,methylnaphthalenes. The naphthalene overhead is withdrawn via line 3dand condensed in cooler 32 to substantially pure naphthalene crystalsmelting at about 80 C. These crystals are normally in excess of 99%pure. The alkylnaphthalene bottoms from column 23 is Withdrawn via line34 and may be sent to dealltylation facilities not shown on the drawingto produce additional naphthalene. Such dealkylation facilities may bethose of any conventional catalytic hydrodealkylation process. Anespecially preferred technique for deallrylating methylnaphthalenesemploys steam and hydrogen at elevated temperatures and pressures over acobalt-molybdate catalyst, as is more particularly described in US.Patent No. 2,734,929 to Doumani. Where the column 23 bottoms product issubjected to deallrylation, the resulting deallcylate can be recycled toadmixture with the feed to column l if desired.

The foregoing is not to be considered limitative of the scope of ourprocess. As those skilled in the art will appreciate, other conventionalazeotropic techniques may be employed, and other conventional methodssuch as fractional crystallization may be employed to recovernaphthalenc from the azeotroping bottoms.

An important advantage not heretofore mentioned of the use of our glycolformates as azeotrope formers, over the used of other materials for thispurpose, is the fact that the glycol formates do not form azeotropeswith naphthalene. This has obvious benefit in that, for one thing, itmakes for easier control in the practice of the process. We have foundthe glycol formates to be noncorrosive to mild steel and this of coursegives them an advantage over competitive azeotrope formers, such as, cg,certain of the organic amine salts. The beneficial aspects of such lackof corrosivity in equipment and preventive maintenance cost savings areobvious. Slight decomposition of the formates occurs on refluxing atatmospheric pressure. However, this can be almost entirely eliminated byoperating at reduced pressures. An additional benefit of the use ofreduced pressures is that improved alphas and azeotropic overheadcompositions are thereby realized.

The glycol formate azeotrope formers of this invention include glycoldiformates, glycol monoformates and mixtures thereof. These esters havebeen found to possess unique superiority as azeotropic agents forseparating naphthalene from other hydrocarbons, in which respect theyare greatly and unexpectedly superior to their acidsubstituted homologs,including even the glycol acetates. The glycol formates of either monoordiformate identity as readily prepared by Well known methods. A simpleway to prepare them is simply to formulate the appropriate glycol, orglycols, with formic acid or formic anhydride. The glycol moieties ofour azeotrope formers can be of any size and character consistent withan operative boiling point level in the azeotrope former. Preferredglycols for purposes of our invention, as determined primarily byboiling point considerations, are those having our carbon atoms or less,typical of which are: ethylene glycol; 2,3-butanediol; 1,4-butanediol;1,3-butanediol; 1,2- butanediol; trimethylene glycol; diethylene glycol;and propylene glycol. As will be apparent from the foregoing list, theclass of glycol formates suitable for use as azeotrope formers in ourinvention includes glycol ether forrnates such as, for example,diethylene glycol formates.

Our preferred azeotrope former, for reasons of ready availability, lowcost and excellence of result, is ethylene glycol diformate. ic /ever,it is within the scope of our 'nventicn, and even preferred in manycases, to employ a mixture of ethylene glycol mono and diformates havingsuitable solubility characteristics for the hydrocarbon stock beingtreated. For highly aromatic stocks, a higher proportion of mono-formatsis normally desirable. In any event, Where such a mixture of formatcs isemployed a ternary azeotrope containing hydrocarbon, monoand di-formateis produced. Other mixtures of individually suitable formates, such asmixtures of monoand diformates and/or glycol formates of differingglycol entities, can likewise be used within the scope of our invention.

The effectiveness of our process is more particularly illustrated by thefollowing examples. These examples are, however, not to be construed aslimitative, but merely exemplary, in purpose.

EXAMPLE I This example is included to illustrate the iner'ficacy ofstraight distillation as a means of separating naphthalenic fromnon-naphthalenic hydrocarbons in admixture therewith.

The 4G0550+ P. fraction of a reformate product was separated therefromby distillation and subjected to a hydrocarbon type analysis. Theresults of the analysis are set forth below.

Components: Percent by Weight Allcanes 7.6

lvionohaphthenes 2.3 Poly-naphthenes 2.1 Alkylbenzenes 22.1Tetralin-indanes 24-. Naphtlialenes 1 37.8

'lhe distribution of the naphthalenes was found to be as follows (thefigures representing weight percentages of the total sample) 7 a :1reflux ratio and in the absence of an azeotroping agent. The fractionsobtained from the batch distillation were analyzed for hydrocarbontypes. Results of these analyses appear in Table 1 below:

"11 till:

subjected to straight batch tion in a -plate Oldershaw column at areflux ratio of The overhead product is a phthalic grade naphthalene of79 C. melting point. The overall recovery of naphthalene is about 88percent.

Table 1 Boiling P0int,F -{400-420 420430 430-435 435-440 440-445445450r450-455 455-450 400-455'405-470470-540 540-550 W'cight percent1s. 5 18.3 5. 07 7.14 5. 65 3. 38 2.04 2. 44 4. 22 13. 3 14. 4s 0.

Alkanes 11. 9 9. 8 9.1 3. 7 8.1 7. 2 3. 5 2. 7 0. 7 'Mono-nephtheues-4.1 4. 4 4. 3 4. 5 4. 0 3. 3 4. e 2.1 1. 4 0.6 Poly-naphthenos. 1. 9 2.2 2. 7 2. 0 2. 8 3.1 2. 9 2. 3 1. 9 0. 7 0. 5 0. 5 Alkylbenzenes 34.134.0 34.2 32.2 23.8 20.1 15.3 10.9 4.4 2.0 3.9 Tetralindndanes. 23. 930. s 39. 0 3s. 9 44. 1 43. 5 41. 7 30. 4 25. s 9.1 4. s 1. 5Naphthalencs 13. 5 19. 2 10. 9 11.0 s. s 9.1 27.1 39. 7 5s. 3 85.1 80.653. 2 C 17.7 18.6 10.2 10.2 6.7 5.1 3.3 2.6 1.7 0.7 3.3 3.0 0.2 0.4 0.50.6 1.8 3.5 23.2 30.5 56.0 33.3 27.3 1.5 41.9 11.6 0.2 0.5 20.2 0.6 7.20.3

In evaluating the Table 1 data, it will be noted that the bulk of allcomponents of the feedstock except the higher boiling alkylnaphthalenesdistilled oil in the fractions within the boiling point range from 400to 450 F. It will be further noted that none of he six fractions withinthat range show any practically significant enrichment in eithernaphthalene or non-naphthalenic hydrocarbons over the starting material.

Turning next to the higher boiling fractions, particularly those between450 and 540 B, it will be observed that no practical selectivity waseffected there either. Thus, while the bulk of the alkylnaphthaleneportion of the feed distilled within that range there was also much'alkylbenzene and tetralin-indane distillation therein to mitigateagainst economically acceptable selectivity. This was particularly trueof the boiling point range from 450 to 465 F.

EXAMPLE TI This is an example of a continuous azeotropic distillation ofa reformate fraction boiling between 469 and 445 F., using a mixture ofethylene glycol monoformate and ethylene glycol diformate, in a weightratio of the former to the latter of one, as the azeotrope former. Here,and elsewhere herein, the term azeotrope former is loosely used toconnote, or generically include, mixtures of glycol formates where suchusage appropriately applies. We also employ the term, where appropriate,to refer to individual glycol formates.

The reformate fraction contains 43 weight percent naphthalene and 1weight percent methylnaphthalene, the remainder being alkanes,naphthenes, alkylbenzenes, tetralins and indanes. The azeotrope formeris employed in a ratio of 80 volumes per 100 volumes of retorrnate feed.The distillation column employed is a conventional vacuum jacketed glassOldershaw column with 66 perforated plates or" 28 mm. 1.1)., each having82 holes or" 0.89 mm.

iameter. The plate to plate spacing is approximately 27 mm. Thedistillation is conducted at a reflux ratio of 5:1.

In carrying out the continuous distillation of this example, thereformate feedstock is continuously introduced into the 60-plateOldershaw column along with a properly proportioned volume of theazeotrope former. The column is operated to produce an overhead vaporstream at a temperature of about 342 F. and a bottoms fraction boilingabove about 425 F. The latter fraction is con tinuously withdrawn fromthe bottom of the Oldershaw column as the process product, and comprisesabout 98 percent by weight naphthalene.

The overhead from the column is condensed and separated into two phasesahydrocarbon phase comprising primarily non-naphthalenic components ofthe feedstock, but including about 2 percent by weight of the azeotropeformer, and a glycol formate phase.

The bottoms product from the azeotropic distillation is The result ofthis example clearly illustrate the excellent selectivity attainablethrough the use of glycol formates as azeotrope formers in the method ofour invention. They also illustrate that such selectivity is notdependent upon the use of large quantities of az-eotrope former but, onthe contrary, that relatively small quantities are sufiicient for thepurpose. Thus, in the present example the ratio of azeotrope former tonon-naphthalene feedstock hydrocarbons, on a volume basis, is only1.4:1.

EXAMPLE III This example demonstrates the superiority of our glycolformates as azeotrope formers over their correspondin acetate esters andalso their superiority over the straigh ycols.

A batch distillation was conducted on a hydrocarbon stock containingnaphthalene, in the presence of ethylene glycol diformate in a ratio of83 volumes of the diformate per volumes of the stock. The hydrocarbonanalysis of the stock showed that it contained 57% non-naphthaleniccompounds.

Two other batch distillations were run, each similar in every respect tothe above-described one except that in one case ethylene glycoldiacetate (instead of ethylene glycol diformate) was employed as theazeotrope former and in the other case propylene glycol was so employed.The amount of hydrocarbon removed as an azeotropic overhead withouttaking naphthalene overhead was determined for each of the three runs asa measure of the selectivity of the azeotrope former tested. The resultsare shown below.

Weight percent of hydrocarbon removed relatively free or" CmHs Azeotropeformer:

Propylene glycol 12 Glycol diacetate 21 Glycol diforrnate 37 The aboveresults clearly illustrate the great superiority of glycol form-atesover the straight glycols as azeotrope formers for our purposes. Theylikewise illustrate that the glycol formates are greatly andunexpectedly superior to their close acetate homologs as selectiveazeotrope formers for use in the process of this invention.

EXAMPLE IV This example is illustrative of the separation ofnonnaphthalenic hydrocarbons from alkylnaphthalenes according to themethod of this invention.

A bottoms fraction of a platinum-catalyzed reformer product have aboiling range of 385-440 F. is hydrodealkylated over a cobaltoxide-molybdenum oxide catalyst to produce a dealkylated product boilingover the range l4l-550 F. This product is fractionally distilled toobtain a light gasoline fraction boiling at l4l401 F., a naphthalenefraction boiling at 40l-438 F., a methylnaphthalene fraction boiling at456-467 F., and a heavy fraction boiling at 493 550 F. Analysis showsthe methylnaphthalene fraction to contain about 90.5 percent by weightof 1- and 2-methylnaphthalenes and about 9.5 percent by weight ofnon-naphthalenic hydrocarbons, presumably allryltetralins andalkylindanes. This material, together with 40 percent by weight ofethylene glycol monoformate, is introduced into a 20 plate Oldershawcolumn and a distillation is carried out therein to yield a bottomsproduct enriched in methylnaphthalenes.

EXAMPLE V This example illustrates an azeotropic distillation accordingto this invention in which propylene glycol diformate is used as theazeotrope former.

A quantity of a reformate fraction containing 43 weight percentnaphthalene and 1 weight percent methylnaphthalene, the remainder beingallranes, naphthenes, alkylbenzenes, tctralins and indanes, togetherwith 30 percent by weight propylene glycol diformate is introduced intoa 40 plate Oldershaw column and a distillation is carried out therein toyield a bottoms product enriched in naphthalene.

EXAMPLE VI This example is illustrative of the separation ofnonnaphthalene hydrocarbons from naphthalene according to the method ofthis invention using a mixture of trimethylene glycol monoformate andl,4-butanediol diforrnate as the azeotrope former.

A quantity of a reformate fraction containing 43 weight percentnaphthalene and 1 weight percent methylnaphthalene, the remainder beingalkanes, naphthenes, alkylbenzenes, tetralins and indanes, together with20 percent by weight of a mixture of trirnethylene glycol monoformateand 1,4-butanediol diformate in a molar proportion of the former to thelatter of one, is introduced into a 40 plate Oldershaw column and adistillation is carried out therein to yield a bottoms product enrichedin naphthalene.

It will be apparent that the method of our invention is applicable foruse in the separation of many hydrocarbon mixtures other than thosedescribed in the above examples. Thus, any hydrocarbon mixture amenableto such treatment within the purview of our invention can be separatedinto non-naphthalenic and naphthalenic fractions by azeotropicallydistilling it in the presence of a suitable glycol formate azeotropeformer in accordance with the teachings herein. Furthermore, theazeotropic distillation technique of this invention can be incorporatedin, or combined with, existing dealkylation methods in a variety of waysto yield a corresponding variety of new processes for the treatment ofhydrocarbon mixtures such as those herein identified as suitablefeedstock materials. Illustrative examples of two such compositeprocesses are described below. It is emphasized that the descriptions ofthese processes are included purely for illustrative purposes and thatno limitative significance should be attached to the particular stepsequences and flow arrangements there disclosed. Many other compositeazeotropic distillation-dealltylation processes within the scope of thisinvention can be readily visualized.

Both of the above-mentioned processes are designed to treat, by acombination of azeotropic distillation and dealliylation techniques,hydrocarbon mixtures boiling within the range from about 39 to about 520F. and containing naphthalene and non-naphthalenic hydrocarbons notseparable therefrom by fractional distillation, as well asalltylnaphthalenes. The object of each process is, of course, to obtainby fractionation and dealkylation means as much naphthalene as possiblefrom the feedstock mixtures.

one of said processes comprises fractionally distilling the feedstock toobtain a first overhead of naphthalcne and non-naphthalenic hydrocarbonsboiling Within the range from about 390 to about 42.5 F. and a firstbottoms product enriched in alkylnaphthalenes boiling with n the rangefrom about 425 to about 520 F; azeotropically distilling said firstoverhead using a glycol formate as the azeotrope former to therebyremove nonnaphthalenic hydrocarbons overhead in the form of anazeotropic distillate and yield a naphthalene-enriched second bottomsproduct; subjecting the first bottoms product to a dealkylationtreatment; fractionally separating the cilluent from said dealkylationtreatment into a light fraction containing gasoline, a heart-cutnaphthalene fraction and a heavy fraction; and recycling said heavyfraction to the dealkylation treatment.

In the second illustrative process the feedstock is fractionated toremove a light gasoline fraction, boiling below about 415 F. anapthalene fraction boiling between about 415 and about 430 F. and aheavy fraction boiling above about 430 P. which is enriched .inalkylnaphthalenes. Said naphthalene fraction is subjected to azeotropicdistillation in accordance with the teachings herein to yield anaphthalene bottoms product and an azeotropic overhead containingnon-naphthalenic hydrocarbons boiling below about 430 E, whichhydrocarbons can be removed by phase separation means and blended withthe aforesaid light gasoline fraction. Said heavy fraction enriched inalkylnaphthalenes is subjected to a dealkylation treatment and thenormally li uid portion of the effluent therefrom is blended with freshfeedstock to the overall process.

As will be evident from the foregoing teachings, the azeotropicdistillation feature of our invention can be viewed either as anindependent entity or as one element of a combination azeotropicdistillation-dealkylation process of the type just described. Thisvantage point distinction is of importance in fixing the breadth of theclass of azeotrope formers in a given embodiment. Thus, when theazeotropic distillation procedure is viewed as an independent entity,the gist of the invention is felt to reside in the use of a particularkind of azeotrope former (from the glycol formate class set forth andclaimed herein) whereas, when it is integrated with a dealkylationprocess and viewed as one element of the resulting combination it isfelt that patentability resides broadly in the combination and not inthe identity of the azeotrope former. Hence, in the former case theclaims are limited to glycol formate azeotrope formers whereas in thelatter case they are not so limited but are broad as to suitableazeotrope formers. Examples of azeotrope formers other than glycolformates which are useful for the dealkylation embodiments of ourinvention are butyrolactone and N-methyl formamide. For detaileddescriptions of the use of these two materials as azeotrope formers forthe separation of non-naphthalenic hydrocarbons from mixtures containingnaphthalene, such as those of present interest, see copending US. patentapplications of Serial Numbers 19,526 and 82,496, filed April 4, 1960,and lanuary 13, 1961, respectively.

We claim:

1. A process for treating a hydrocarbon mixture boiling within the rangefrom about 390 F. to about 520 F, and comprising naphthalenic andnon-naphthalenic components which are not separable by simple fractionaldistillation, which comprises: azeotropically distilling said mixturetogether with a glycol formate to vaporize said non-naphthaleniccomponents together with said glycol formate as a minimum boilingazeotropic distillate; and recovering as azeotropic bottoms a product inwhich the ratio of naphthalenic to non-naphthalenic hydrocarbons issubstantially greater than the ratio thereof in said hydr carbonmixture.

2. The process of claim 1 wherein said hydrocarbon mixture boilingwithin the range from about 390 to about 520 F. has a boiling rangespread no greater than about Fahrenheit degrees.

s,114,es0

3. A process as defined by claim 1 wherein said naphthalenic componentsof said hydrocarbon mixture include naphthalene.

4. The process of claim 1 wherein the glycol portion of the glycolformate has no more than four carbon atoms.

5. The process of claim 1 wherein said glycol formate is ethylene glycoldiformate. 6. The process of claim 1 wherein said glycol formate is amixture of a major proportion of ethylene glycol monoforniate and aminor proportion of ethylene glycol diformate.

7. A process for treating a hydrocarbon mixture boiling within the rangefrom about 390 F. to about 520 F, and having a boiling range spread nogreater than about 50 Fahrenheit degrees, comprising naphthalenic andnonnaphthalenic hydrocarbons which are not readily separable by simplefractional distillation means, comprising: (1) subjecting a mixture ofsaid hydrocarbon mixture and a formate carbon atoms to a firstdistillation under conditions such as to separate therefrom a firstazeotropic distillate, consisting essentially of non-napthalenichydrocarbons together with the glycol formate, and a liquid bottomsfraction enriched in napthalenic hydrocarbons; (2) condensing said firstdistillate and allowing it to separate into two liquid phases, a firstphase comprising glycol formate and a minor proportion ofnon-naphthalenic hydrocarbons and a second phase comprisingnon-naphthalenic hydrocarbons and a minor proportion of glycol formate;(3) returning said first phase to said first distillation; (4)subjecting said second phase to a second distillation to obtain a secondazeotropic distillate of glycol formate and non-naphthalenichydrocarbons and a bottoms product comprising non-napthalenichydrocarbons; and (5) combining said second azeotropic distillate withsaid first azeotropic distillate.

8. A process as defined by claim 7 wherein said naphthalenic fraction ofsaid hydrocarbon mixture includes naphthalene.

9. A process as defined by claim 7 wherein said nonnaphthalenic fractionof said hydrocarbon mixture includes at least one hydrocarbon type fromthe class consisting of alkylbenzenes, alkyltetralins and alkylindanes.

10. The process of claim 7 wherein said glycol formate is ethyleneglycol diformate.

11. The process of claim 7 wherein said glycol formate is a mixture of amajor proportion of ethylene glycol monoformate and a minor proportionof ethylene glycol diformate.

12. A method for the recovery of substantially pure naphthalene from apetroleum fraction comprising naphthalem'c and non-naphthaleniccomponents not readily separable by simple fractional distillation,boiling above about 400 R, which comprises: (1) subjecting said fractionto azeotropic distillation in admixture with a formate of a glycolhaving no more than four carbon atoms until of a glycol having no morethan four 12 a major proportion of the non-naphthalenic hydrocarbons insaid fraction which boil within about 10 Fahrenheit degrees ofnaphthalene is distilled overhead with said glycol formate as anazeotropic distillate; and (2) recovering substantially pure naphthalenefrom the remaining bottoms fraction of said azeotropic distillation.

13. The method of claim 12 in which said non-naphthalenic componentsinclude alkylbenzenes, alkyltetralins and alkylindanes boiling withinthe range from about 410 F. to about 435 F.

14. The method of claim 12 in which said petroleum fraction is a heavynaphtha reformate including a naphthalene fraction boiling over therange from about 410 F. to about 450 F.

15. The method of claim 12 in which said petroleum fraction is a heavynaphtha reformate which has been subjected to catalytichydrodealkylation and which includes a naphthalene fraction boilingwithin the range from about 410 F. to about 450 F.

16. The method of claim 12 in which said glycol formate comprisesethylene glycol diformate.

17. A method for the recovery of substantially pure naphthalene from apetroleum distillate including a naphthalene fraction boiling within therange from about 410 F. to about 450 F., said naphthalene fraction alsocontaining alkylbenzenes, alkyltetralins and alkylindanes, whichcomprises: (1) subjecting said fraction to azeotropic distillation inadmixture with a formate of a glycol having no more than four carbonatoms until substantially all of the non-naphthalenic hydrocarbons insaid fraction which boil within about 20 Fahrenheit degrees ofnaphthalene are distilled overhead as an azeotropic distillate with theglycol formate; and (2) distilling the remaining bottoms fraction fromsaid azeotropic distillation in the absence of glycol formate to recoversubstantially pure naphthalene as an overhead product.

18. The method of claim 17 in which said petroleum distillate is a heavynaphtha reformate which has been subjected to catalytichydrodealltylation and which boils above about 400 F.

19. The method of claim 17 in which said glycol formate is a mixture ofa major proportion of ethylene glycol monoformate and a minor proportionof ethylene glycol diformate.

20. The method of claim 17 in which said petroleum distillate is a heavynaphtha reformate boiling above about 400 F.

References Cited in the file of this patent UNITED STATES PATENTS2,734,929 Doumani Feb. 14, 1956 3,043,890 McKinnis July 10, 1962 FORElGNPATENTS 209,041 Australia June 26, 1957 456,616 Canada May 10, 19491,037,756 France May 6, 1953

1. A PROCESS FOR TREATING A HYDROCARBON MIXTURE BOILING WITHIN THE RANGEFROM ABOUT 390*F. TO ABOUT 520* F., AND COMPRISING NAPHTHALENIC ANDNON-NAPHTHALENIC COMPONENTS WHICH ARE NOT SEPARABLE BY SIMPLE FRACTIONALDISTILLATION, WHICH COMPRISIES: AZEOTROPICALLY DISTILLING SAID MIXTURETOGETHER WITH A GLYCOL FORMATE TO VAPORIZE SAID NON-NAPHTHALENICCOMPONENTS TOGETHER WITH SAID GLYCOL FORMATE AS AMINIMUM BOILINGAZEOTROPIC DISTILLATE; AND RECOVERING AS AZEOTROPIC BOTTOMS A PRODUCT INWHICH THE RATIO OF NAPHTHALENIC TO NON-NAPHTHALENIC HYDROCAROBNS ISSUBSTANTIALLY GREATER THAN THE RATIO THEREOF IN SAID HYDROCARBONMIXTURE.